This invention relates to an internal combustion engine equipped with fuel injectors for supplying fuel into the cylinders of the engine, and more particularly to an internal combustion engine equipped with main and auxiliary fuel injectors in order to supply the cylinders of the engine with suitable amounts of fuel.
It is well known in art, that only one fuel injector is installed at the intake passageway of the engine to supply the cylinders of the engine with fuel injected from the fuel injector. This fuel injector is, in general, composed of an electromechanical valve which is arranged to open to inject fuel during the time period corresponding to the pulse-width determined in accordance with various engine operating parameters. Accordingly, the amount of fuel supplied to the cylinders is in proportion to the pulse-width.
In such a fuel injector, the opening area of the electromechanical valve is set to meet the maximum fuel supply amount required, for example, during the maximum power output engine operation in which the above-mentioned pulse-width is the maximum or the electromechanical valve is continuously maintained at the fully open condition.
Hence, the above-mentioned pulse-width for controlling the fuel injector must be small during a relatively low power output engine operation in which a relatively small amount of intake air is required, particularly during idling of the engine. The accuracy of the electromechanical valve of the injector depends on the actuation lag time due to the friction of the mechanical parts of the valve. The actuation lag time is, for example, about 1.6 ms from the closed condition to the open condition, and about 0.9 ms from the open condition to the closed condition.
Therefore, the extreme fluctuation of the opening time of the electromechanical valve is encountered during the low power output engine operation in which the opening time or the pulse-width for controlling the valve is shorter than about 2 to 2.5 ms. This shows that it is difficult to maintain a high accuracy in fuel supply amount regulation during such the low engine power output engine operation. This difficulty increases with increase in the number of the cylinders of the engine and with increase in the total volume of the engine cylinders.